Reland of Teach bot_update to support patching deps in solutions other than the patch_root

Reland of Teach bot_update to support patching deps in solutions other than the patch_root

Original CL: https://codereview.chromium.org/552763002/
With one fix - patch_root is sometimes None, so it should be defaulted to a string
so that string concat doesn't raise an error.

BUG=411434
Committed: http://src.chromium.org/viewvc/chrome?view=rev&revision=291864

[Ryan Tseng, 2014-09-08 20:43:32]

hinoka@google.com changed reviewers:
+ agable@chromium.org, hinoka@google.com, iannucci@chromium.org

[Ryan Tseng, 2014-09-08 20:43:33]

PS1 = old CL, PS2 = this CL

[agable, 2014-09-08 20:46:36]

On 2014/09/08 20:43:33, Ryan T. (EMEA time) wrote:
> PS1 = old CL, PS2 = this CL

Oof, really? Gross. I hope no one ever creates a solution with path ''.

[agable, 2014-09-08 20:46:42]

On 2014/09/08 20:46:36, agable wrote:
> On 2014/09/08 20:43:33, Ryan T. (EMEA time) wrote:
> > PS1 = old CL, PS2 = this CL
> 
> Oof, really? Gross. I hope no one ever creates a solution with path ''.

Oh and also lgtm.

[Ryan Tseng, 2014-09-08 20:51:09]

The CQ bit was checked by hinoka@google.com

[commit-bot: I haz the power, 2014-09-08 20:51:54]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/hinoka@chromium.org/549223003/20001

[commit-bot: I haz the power, 2014-09-08 20:53:31]

Committed patchset #2 (id:20001) as 291864